Interest in the use of liquid natural gas (LNG) as a fuel for motor vehicles has increased dramatically in recent years. LNG is relatively inexpensive and provides an alternative to fuel oil from foreign sources. In addition, it burns very cleanly, making it much easier for fleets to meet more restrictive pollution emission standards. A rail locomotive is one type of vehicle that utilizes LNG as a fuel. The rail locomotive hauls a tender car, or rail tender, that contains the locomotive's LNG for fuel. There are various ways to provide the LNG from the rail tender to the locomotive's engine.
One way is to provide a pump that is submersed within LNG in a tank of the rail tender. The pump is configured to pump the LNG to the locomotive when pressure within the tank is insufficient to drive LNG to the engine based on pressure alone. When pressure in the tank is sufficient, LNG can be driven to the locomotive by tank pressure alone through the pump. Such systems include an economizer circuit that is used to relieve high pressure within the tank. The economizer circuit typically includes a regulator that allows vapor from the tank to be delivered to the locomotive when the pressure in the tank rises above a predetermined level. By pulling vapor from the tank, the pressure in tank falls dramatically and pressure within the tank is relieved.
Another type of system is a saturation delivery style system that requires the LNG to be saturated (warmed) to a boiling pressure slightly above the operational input pressure to the engine, which may be in the range of 125-135 psig for example. Once saturated, the LNG is of sufficient pressure to enable pressure transfer of the LNG to the locomotives of the rail system. Such systems can also include an economizer system.
There are advantages and disadvantages to both a pump style delivery system and a saturation delivery style. In view of this, there is a need for improved systems and methods for delivering gas in a rail car system that combines various modes of delivering cryogenic fuel to a use device.